The present invention relates to a welding wire containing a flux.
U.S. Pat. No. 6,153,847 discloses a welding wire containing a flux filled in the outer layer of a welding metal to improve mechanical properties, crack resistance, etc. of the welded metal. The flux contains various materials including a deoxidizer, a slag forming agent, an arc stabilizer and metal powder. In such a welding wire, since an arc occurs between the metal outer layer and a base material to be welded, the metal outer layer is first melted. For this reason, the flux located in the central portion of the outer layer cannot be melted sufficiently and thus the arc tends to be unstable. As a result, spatters tend to be easily generated with reduced work efficiency. Particularly, a welding wire made of Ni or an Ni-based alloy has such a problem, because the melting point of Ni or Ni-based alloy is lower than that of iron or the like. Further, the tubular outer layer is formed by rounding a plate metal material. If the thickness of the outer layer is larger than a predetermined value, the plate metal material cannot be formed into a tubular shape. For this reason, there is a limitation on reducing a flux filling space inside of the outer layer and thus the amount of flux content cannot be adjusted at a lower level. When the amount of the flux is increased to a level more than necessary, impurities included in the flux cause the welding metal to tend to crack. To avoid this, a structure was proposed wherein an electrically conductive core wire 103 supported by a support 102a integrally formed with a metal outer layer 102 is arranged nearly in the center of a flux 101, as shown on page 73 in a book entitled xe2x80x9cLatest Welding Technology (Edition 2)xe2x80x9d issued by Corona Publishing Co., Ltd., Japan, 1998, and written by Haruyoshi Suzuki (refer to FIG. 5). When the core wire 103 is disposed in the outer layer, an arc occurs between the core wire 103 and a base material to be welded and melting of the flux 101 is promoted, thus stabilizing the arc. Further, a flux filling space inside of the metal outer layer 102 can be decreased and thus cracking of the welded metal can be suppressed by suitably adjusting the amount of flux.
However, in order to support the core wire 103, such a welding wire requires complicated forming of the support 102a in the metal outer layer 102. In particular, when the diameter of the welding wire is 2.0 mm or less, the manufacturing steps become more complex.
It is therefore an object of the present invention to provide a welding wire containing a flux, in which an electrically conductive core wire made of Ni or Ni-based alloy can be disposed without the need for performing complicated manufacturing steps at a metal outer layer made of Ni or Ni-based alloy.
In accordance with an aspect of the present invention, a flux-contained welding wire is provided that includes a metal outer layer of a pipe shape made of Ni or Ni-based alloy, a flux filled inside of the metal outer layer, and an electrically conductive core wire made of Ni or Ni-based alloy and disposed inside of the metal outer layer together with the flux. In this case, the conductive core wire is disposed without being supported by the metal outer layer and such an amount of the metal powder is included in the flux as to reduce an electric resistance value between the metal outer layer and conductive core wire so that an arc can occur between the conductive core wire and a base material to be welded. In this context, the wording xe2x80x9cwithout being supported by the metal outer layer xe2x80x9d means that the conductive core wire is substantially separated from the metal outer layer, not being substantially connected to or engaged with the metal outer layer, for example, as shown in FIG. 5. However, a welding wire having the conductive core wire partly contacted with the metal outer layer is included in the scope of the present invention, because the conductive core wire is not mechanically or directly supported by the metal outer layer. In the present invention, electrical conduction between the metal outer layer and conductive core wire is realized by the flux metal powder of such an amount that can lower the electric resistance value between the metal outer layer and conductive core wire. As a result, even when the conductive core wire is arranged inside of the metal outer layer together with the flux without being supported by the metal outer layer, the electrical conduction of the conductive core wire with the metal outer layer via metal powder within the flux enables an arc to occur between the conductive core wire and a base material to be welded. The welding wire of the present invention can be manufactured more easily than the conventional welding wire which needs complicated manufacturing steps in order to support the conductive core wire by the outer layer. In particular, when the average outer diameter of the metal outer layer is 2.0 mm or less, great effect can be obtained by the present invention.
An amount of metal powder can be set to 20-80 weight % of granular metal powder per a weight of the flux in order to reduce the electric resistance value between the metal outer layer and conductive core wire to such a level that an arc can be generated between the conductive core wire and a base material to be welded. When the metal powder is of a granular type, the metal powder can be advantageously dispersed and mixed into the flux substantially homogeneously. When the amount of granular metal powder does not exceed 20 weight %, the conductivity between the metal outer layer and conductive core wire cannot be sufficiently increased by the flux and thus a sufficient arc cannot be generated between the conductive core wire and a base material to be welded. For this reason, the arc state becomes bad and spatters tend to be easily generated. Further, when the amount of metal powder exceeds 80 weight %, the necessary amount of non-metal flux such as an arc stabilizer is decreased. As a result, the arc state becomes bad and spatters tend to be easily generated.
When the weight % of the weight of the flux to the weight of the welding wire per unit length is set in a range of 6.5-30 weight %, the effect of the flux can be enhanced and cracking of the welded metal can be suppressed. When the weight % is less than 6.5 weight %, the effect of the flux acting to improve the mechanical properties, crack resistance, etc. of the welded metal cannot be obtained. When the weight % exceeds 30 weight %, the impurities contained in the flux tend to cause the welded metal to be easily cracked. Further, it is difficult to arrange the conductive core wire in the flux.
When the weight % of the weight of conductive core wire to the weight of the welding wire per unit length is set in a range of 1.5-15 weight %, the arc can be made stable and spatters tend to be less often generated. When the weight % is smaller than 1.5 weight %, the arc generation by the conductive core wire becomes insufficient with the result that an arc becomes unstable and spatters tend to be easily generated. When the weight % exceeds 15 weight %, the amount of the flux is limited and the necessary amount of non-metal flux such as an arc stabilizer is decreased. As a result, the arc state becomes had and spatters tend to be easily generated.
As the main component of the metal powder included in the flux, Ni or Ni-based alloy powder can be employed.
The average particle diameter of the Ni or Ni-based alloy powder is preferably 10-100 xcexcm. The average outer diameter of the metal outer layer is preferably not larger than 2.0 mm.
The conductive core wire may have various sectional shapes of polygon, circle, etc. When the conductive core wire has a sectional shape of a nearly circle, the arc state can be made good.
In the case of a specific flux-contained welding wire according to the present invention, the amount of metal powder included in the flux is 50-60 weight %, the weight % of the weight of the flux to the weight of the welding wire per unit length is 15.5-19.5 weight %, and the weight % of the weight of the conductive core wire to the weight of the welding wire per unit length is 3.5-7.5 weight %. When the amount of the metal powder and the weight % of the flux and core wire are set in the aforementioned value ranges, the most desirable effect of the flux can be obtained.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.